Earth-boring tools are commonly used for forming (e.g., drilling and reaming) bore holes or wells (hereinafter “wellbores”) in earth formations. Earth-boring tools include, for example, rotary drill bits, coring bits, eccentric bits, bi-center bits, reamers, under-reamers, and mills.
Different types of earth-boring rotary drill bits are known in the art including, for example, fixed-cutter bits (which are often referred to in the art as “drag” bits), rolling-cutter bits (which are often referred to in the art as “rock” bits), superabrasive-impregnated bits, and hybrid bits (which may include, for example, both fixed cutters and rolling cutters). The drill bit is rotated and advanced into the subterranean formation. As the drill bit rotates, the cutters or abrasive structures thereof cut, crush, shear, and/or abrade away the formation material to form the wellbore.
The drill bit is coupled, either directly or indirectly, to an end of what is referred to in the art as a “drill string,” which comprises a series of elongated tubular segments connected end-to-end that extends into the wellbore from the surface of the formation. Various tools and components, including the drill bit, are often coupled together at the distal end of the drill string at the bottom or end of the wellbore being drilled. This assembly of tools and components is referred to in the art as a “bottom hole assembly” (BHA).
The drill bit may be rotated within the wellbore by rotating the drill string from the surface of the formation, or the drill bit may be rotated by coupling the drill bit to a downhole motor, which is also coupled to the drill string and disposed proximate the bottom of the wellbore. The downhole motor may comprise, for example, a hydraulic Moineau-type motor having a shaft, to which the drill bit is attached, that may be caused to rotate by pumping fluid (e.g., drilling mud or fluid) from the surface of the formation down through the center of the drill string, through the hydraulic motor, out from nozzles in the drill bit, and back up to the surface of the formation through the annular space between the outer surface of the drill string and the exposed surface of the formation within the wellbore.
Superabrasive-impregnated earth-boring rotary drill bits and other tools may be used for drilling hard or abrasive rock formations such as sandstones. Typically, a superabrasive-impregnated bit has a solid body, which is often referred to in the art as a “crown,” that is cast in a mold. The crown is attached to a steel shank having a threaded end that may be used to attach the crown and steel shank to a drill string. The crown may have a variety of configurations and generally includes a cutting face comprising a plurality of cutting structures, which may comprise at least one of cutting segments, posts, and blades. The posts and blades may be integrally formed with the crown in the mold, or they may be separately formed and attached to the crown. Channels separate the posts and blades to allow drilling fluid to flow over the face of the bit.
Superabrasive-impregnated drill bits may be formed such that the cutting face of the drill bit (including the segments, posts, blades, etc.) comprises a particle-matrix composite material that includes superabrasive particles dispersed throughout a matrix material. The superabrasive particles may comprise diamond or cubic boron nitride. The matrix material itself may comprise a particle-matrix composite material. For example, the superabrasive particles may be embedded in a material that includes tungsten carbide particles embedded within a metal matrix, such as a copper-based metal alloy.
While drilling with a superabrasive-impregnated drill bit, the matrix material surrounding the superabrasive particles wears at a faster rate than do the superabrasive particles. As the matrix material surrounding the superabrasive particles on the surface of the bit wears away, the exposure of the superabrasive particles at the surface gradually increases until the superabrasive particles eventually fall away from the drill bit. As some superabrasive particles are falling away, others that were previously completely buried in the matrix material become exposed at the surface of the matrix material, such that fresh, sharp superabrasive particles are continuously being exposed and used to cut the earth formation.
Typically, a superabrasive-impregnated bit is formed by mixing and distributing superabrasive particles (e.g., diamond particles or cubic boron nitride particles) and other hard particles (e.g., tungsten carbide particles) in a mold cavity having a shape corresponding to the bit to be formed. The particle mixture is then infiltrated with a molten metal matrix material, such as a copper-based metal alloy. After infiltration, the molten metal matrix material is allowed to cool and solidify. The resulting superabrasive-impregnated bit may then be removed from the mold. Alternatively, a mixture of superabrasive particles, hard particles, and powder matrix material may be pressed and sintered in a hot isostatic pressing (HIP) process to form superabrasive-impregnated blades, posts, or other segments, which may be brazed or otherwise attached to a separately formed bit body.